GB2139202A

GB2139202A - Sulphur cements, sulphur concretes, their preparation and use

Info

Publication number: GB2139202A
Application number: GB08311279A
Authority: GB
Inventors: Frederick William Parrett; Brian Robert Currell
Original assignee: SEATON CHEMICAL DEVELOPMENTS L
Current assignee: SEATON CHEMICAL DEVELOPMENTS L
Priority date: 1983-04-26
Filing date: 1983-04-26
Publication date: 1984-11-07
Also published as: GB2139202B; GB8311279D0

Abstract

Sulphur cements and concretes are made by heating together sulphur, a plasticiser therefor such as dicyclopentadiene, a filler such as pulverised fly ash or silica flour, and a minor proportion of a vulcanisation accelerator as used in the rubber industry. For a sulphur concrete an aggregate may also be present or the other ingredients may be added to heated aggregate.

Description

SPECIFICATION Sulphur cements, sulphur concretes, their preparation and use This invention relates to sulphur cements and sulphur concretes, to methods of preparing them and to their use.

Sulphur concretes are prepared by mixing an aggregate, such as sand or gravel, with a filler, such as silica flour, limestone flour or pulverised fuel ash (fly ash). The mixture is heated to a temperature of, for example, 170 C. and plasticised sulphur is added.

The sulphur melts to form a thermoplastic mass which sets on cooling and which can be used for various purposes, particularly where acid-resistant constructions, floors or linings are required. Sulphur concrete also has the advantage over Portland cement concrete that it reaches its design strength as soon as it has cooled to ambient temperature, usuaily in about 2 or 3 hours, and it is thus useful where quick constructions are required.

In order to prevent the molten sulphur from reverting to its orthorhombic crystalline form on cooling, whereby the sulphur would become powdery and the concrete would become friable, it is necessary to "plasticise" the sulphur so that the final concrete retains its strength and durability. The plasticisation of the sulphur is effected by heating the sulphur with a plasticiser therefor. Many plasticisers for sulphur have been described in the literature; most of them are olefinic liquids which do not substantially volatilise at temperatures below about 140"C. A preferred plasticiser for sulphur is dicyclopentadiene (hereinafter referred to as DCPD) as this is relatively cheap and effective, but others may be used.

In order to plasticise the sulphur it is necessary to heat the su I p h u r with the plasticiser at a temperature in the region of 140"C. for at least 3 hours. Care is needed to control the plasticisation for if the heating is effected too fast or at too high a temperature, the resulting product becomes too viscous to use and gels.

We have now discovered a method of reducing considerably the period required for the plasticisation of the sulphur which method is easier to control and reduces the risk of the occurrence of vicosity problems.

Accordingly, the present invention broadly provides a method of making a sulphur cement or sulphur concrete, wherein sulphur, a plasticiser therefor and a filler are heated together with a minor proportion of a vulcanisation accelerator as used in the rubber industry. The invention also resides in a sulphur cement or sulphur concrete produced by this method.

The use of the vulcanisation accelerator enables the period required for plasticisation to be reduced from about 3 hours to about half an hour whereby considerable savings in the heat requirements of the plasticisation may be achieved. Also the presence of the filler and, optionally the aggregate, which acts as a heat sink makes the plasticisation process easier to control.

The present method may be carried out in two ways. In the first, the aggregate and filler are, in conventional manner, heated to about 1700C. in a mastic mixer or other mixing vessel and then the sulphur, plasticiser and vulcanisation accelerator are added and the mixture is mixed while holding the temperature at 140" to 1 50"C. for at least 30 minutes.

The resulting sulphur concrete is then ready for use.

It is convenient to prepare the sulphur, plasticiser and vulcanisation accelerator for use in this method by mixing these ingredients and placing them in bags of low melting polyethylene, the sulphur being unplasticised at this stage. On site where the sulphur concrete is to be used, the aggregate and filler are heated in a mastic mixer and the requisite number of bags of sulphur mixture is added, the polyethylene melting and becoming incoporated in the concrete without detriment thereto.

However, this way of carrying out the present method may suffer from the disadvantage that heatable mastic mixers or the like which are relatively large and cumbersome pieces of apparatus may be readily available on site. In order to avoid the necessity for using a master mixer on site, in the second way of carrying out the present method, the sulphur, plasticiser, vulcanisation accelerator and at least a major proportion of the amount of filler required in the final product are heated. The filler may be heated to about 170"C. and the sulphur then added or alternatively the filler and sulphur may be mixed cold and then heated to about 140"C., in each case giving rise to a molten mass to which the plasticiser and vulcanisation accelerator are added.

The resulting mass is held at a temperature of 140 to 1 50"C. for at least 30 minutes while mixing and is then poured into trays to set. The resulting solid is ground to small lumps, preferably 6.35mm. and bagged ready for use. In this form the material is a sulphur cement which can be used as such for a variety of purposes or it can be mixed with heated aggregate to form a sulphur concrete. In the latter case, the sulphur cement can be mixed directly with heated aggregate and used direct from a pugmill which is easier and more convenient to use on site.

The sulphur cement in molten form can be brushed onto tanks to form acid-resistant linings or can be used with a reinforcing material such as fibre-glass to form acid-resistant articles. Thus sheets of fibre-glass may be laminated with the sulphur cement to form the articles such as pipes, tanks and other plant items. Another aspect of the invention resides in such articles made from the sulphur cement aforesaid and reinforcing material.

An advantage of heating the sulphur and plasticiser with the filler is that the filler acts as a heat-sink to prevent overheating of the final product so as to reduce the risk of gelling and viscoxity problems and makes the plasticisation easier to control.

As indicated above, plasticisers for sulphur are well known and DCPD is the preferred plasticiser. It is also possible to use, wholly or in part, so-called DCPD residues which are the bottoms obtained in the purification of DCPD by distillation. Other olefinic hydrocarbons which do not substantially volatilise below about 140"C. may be used either alone or in combination with DCPD and will be selected on the basis of efficacy, cheapness and availability.

The vulcanisation accelerators which may be used in the present method are those known for use in the vulcanisation of rubber. Zinc diethyldithiocarbamate (hereinafter referred to as ZDC) is a preferred vulcanisation accelerator and may be used alone or more preferably in conjunction with zinc oxide (ZnO) since the latter is considerably cheaper than ZDC.

Other vulcanisation accelerators which may be used include tetramethyl thiuram disulphide (TMT) and zinc mercaptobenzothiazole (ZMBT).

The sulphur which is used in the present method is that conventionally used in forming sulphur cements and concretes, but we have found that it is possible to replace up to 50% by weight of the sulphur by a waste material which is the filter cake used as a filtration medium in the chemical industry and which contains up to 80% by weight of sulphur and possibly keiselguhr.

The proportions of aggregate (when present), filler, sulphur and plasticiser are typically those used in conventional sulphur cement and sulphur concrete formulations.

For a sulphur concrete, the amount of sulphur present will generally be from 10 to 15% by weight based on the weight of the final product, including aggregate and filler. The plasticiserwill be present in an amount of 1 to 7%, preferably 5%, by weight based on the weight of the sulphur and the vulcanisation accelerator will be present in an amount of up to a few tens of parts per 1000 parts by weight of sulphur. Thus where the vulcanisation accelerator is ZDC + ZnO, the ZDC may be present in an amount of 1 to 20, preferably 3, parts by weight per 1000 parts by weight of sulphur and the ZnO may be present in an amount of 1 to 40, preferably 6, parts by weight per 1000 parts by weight of sulphur.

Four a sulphur cement, the amount of sulphur will be substantially 30 to 70%, preferably about 60%, by weight and correspondingly substantially 70 to 30%, preferably about 40%, by weight of filler. The proportions by weight of the plasticiser and vulcanisation accelerator being based on the sulphur will be the same as those just given.

Although vulcanisation accelerators are known for speeding up the vulcanisation (hardening) of rubber by sulphur, it is considered surprising that they should effectively promote the reverse effect in facilitating the plasticisation (softening) of sulphur by olefinic plasticisers. The use of the vulcanisation accelerators considerably reduces the time and energy required to effect the plasticisation and the presence of the filler either alone or together with the aggregate during the plasticisation makes the plasticisation easier to control. Furthermore, the presence of the vulcanisation accelerator has surprisingly been found to enable the compressive strengths of the resulting sulphur cements or concretes to be achieved by a much shorter period of heating than in the absence of the vulcanisation accelerator.

The invention will now be illustrated by the following Examples.

Example 7 A modified coated sulphur was prepared by mixing sulphur (solid, 1,000 kilos) with zinc diethyl dithiocarbamate (2.73 kilos), zinc oxide (5.45 kilos) and dicyclopentadiene (liquid, 54.5 kilos). Afterthorough mixing, the resulting coated sulphur was placed in preweighed amounts into low melt, polyethylene bags which were then heat sealed, the sulphur being unplasticised at this stage.

Sulphur concrete was prepared from the above modified coated sulphur using a hot mix asphalt plant to heat an aggregate mixture (710 kilos) to 170"C, discharging to a pugmill, where the modified coated sulphur (190 kilos) in low melt bags was added, followed by a filler (pulverised fuel ash, 100 kilos). The molten sulphur concrete was transferred from the pugmill to a heated mastic mixer where it was held for at least 30 minutes at 140 to 1 50"C.

before being poured into place.

Samples of concrete made thus were found to have compressive strengths of 35 - 50 N/mm2, compared to 20 - 30 N/mm2 if the zinc diethyl dithiocarbamate and zinc oxide were omitted.

Example 2 Afiller (pulverised fuel ash, or limestone powder, or silica flour) of less than 200 mesh (40 kilos) was heated to 170"C. in a drum heater. Sulphur (powder, 60 kilos) was added and heating continued as necessary to give a molten mortar-like mixture at 140 - 150"C. Dicyclopentadiene (liquid, 3.2 kilos) was added together with zinc diethyl dithiocarbamate (0.16 kilos) and zinc oxide (0.32 kilos). The mixture was maintained at 140 - 1 50"C. for at least 30 minutes and then poured into metal trays to cool. The resulting solid sulphur cement was crushed and bagged.

The sulphur cement (prepared as above) was used to prepare sulphur concrete using a hot mix asphalt plant by heating an aggregate mixture (780 kilos) to 1700C. discharging to a pugmill, where the sulphur cement (320 kilos) was added in low melt bags. A molten concrete was produced which was ready for immediately pouring into place.

Example 3 The sulphur cement prepared in Example 2 can be made using low grade sulphur waste products, such as filter cake. In this Example, sulphur (30 kilos) and filter cake (37.5 kilos, 80% sulphur) were added to filler (pulverised fuel ash, 32.5 kilos) heated to 1700C. To the resulting molten mixture were added dicyclopentadiene t3.2 kilos), zinc diethyl dithiocarbamate (0.16 kilos) and zinc oxide (0.32 kilos). After at least 30 minutes at 140 - 1 50"C. the mixture was poured into metal trays to solidify.

Example 4 The sulphur cement of Examples 2 and 3 can be used to prepare laminated products. In this Example a laminated sheet was prepared by brushing or spraying the sulphur cement onto layers of glass fibre mat. Four layers of mat produced a test slab 100mm x450mm x 12mm. This slab when supported between 400mm centres required a loading of 53 kilos to fracture it at the centre.

Claims

1. A method of making a sulphur cement or sulphur concrete, wherein sulphur, a plasticiser therefor and a filler are heated together with a minor proportion of a vulcanisation accelerator as used in the rubber industry.

2. A method as claimed in Claim 1, wherein the ingredients are heated together at a temperature of 140 to 150"C. for at least 30 minutes.

3. A method as claimed in Claim 1 or 2 for making a sulphur concrete, wherein the filler and an aggregate are heated and the sulphur, plasticiser and vulcanisation accelerator are added to the heated aggregate and filler.

4. A method as claimed in Claim 3, wherein the sulphur, plasticiser and vulcanisation accelerator are prepared by mixing and are placed in bags of low-melting plastics, and wherein the requisite number of bags of mixture is added to the heated aggregate and filler.

5. A method as claimed in Claim 1 or 2, wherein the sulphur, plasticiser, vulcanisation accelerator and at least a major proportion of the filler required in the final product are heated, allowed to set and ground to form a sulphur cement.

6. A method as claimed in Claim 5 for making a sulphur concrete, wherein aggregate is heated together with any further filler required and the resulting sulphur cement is added thereto.

7. A method as claimed in Claim 5 or 6, wherein the heated mixture is poured into trays to set and ground to lumps about 6.35mm in size.

8. A method as claimed in any one of Claims 1 to 8, wherein the sulphur plasticiser is an olefinic hydrocarbon which does not substantially volatilise below 140"C.

9. A method as claimed in any one of Claims 1 to 9, wherein the sulphur plasticiser is dicyclopentadiene or a dicyclopentadiene residue.

10. A method as claimed in any one of Claims 1 to 9 wherein the vulcanisation accelerator is selected from zinc diethyldithiocarbamate, alone or in conjunction with zinc oxide, tetramethyl thiuram disulphide and zinc mercaptobenzothiazole.

11. A method as claimed in any one of Claims 1 to 10, wherein the filler is pulverised fuel ash, limestone powder or silica flour.

12. A method as claimed in any one of Claims 1 to 11,wherein up to 50% by weight of the sulphur is a sulphur-containing waste material which is a filter cake used as a filtration medium and which comprises up to 50% by weight of sulphur and possibly kieselguhr.

13. A method as claimed in any one of Claims 1 to 12 formaking a sulphur concrete, wherein the sulphur is present in an amount of from 10 to 15% by weight based on the weight of the final product.

14. A method as claimed in any one of Claims 1 to 12 for making a sulphur cement, wherein the sulphur is present in an amount of from substantially 30 to 70% by weight.

15. A method as claimed in any one of claims 1 to 14, wherein the sulphur plasticiser is present in an amount of from 1 to 17% by weight based on the weight of the sulphur.

16. A method as claimed in any one of Claims 1 to 15, wherein the sulphur plasticiser is present in an amount of 5% by weight based on the weight of the sulphur.

17. A method as claimed in any one of Claims 1 to 16, wherein the vulcanisation accelerator is present is an amount of up to 60 parts by weight per 1000 parts by weight of sulphur.

18. A method as claimed in Claim 17, wherein the vulcanisation accelerator comprises, per 1000 parts by weight of sulphur, from 1 to 20 parts by weight of zinc diethyldithiocarbamate and from 1 to 40 parts by weight of zinc oxide.

19. A method as claimed in Claim 18, wherein the vulcanisation accelerator comprises, per 1000 parts by weight of sulphur, 3 parts by weight of zinc diethyldithiocarbamate and 6 parts by weight of zinc oxide.

20. A method of making a sulphur cement or sulphur concrete substantially as hereinbefore described in any one of Examples 1 to 3 of the foregoing Examples.

21. A sulphur cement or sulphur concrete made by the method claimed in any one of Claims 1 to 20.

22. The use of the sulphur cement claimed in claim 21 to form acid-resistant linings.

23. Atank having an acid-resistant lining ofthe sulphur cement claimed in Claim 21.

24. The use of sulphur cement claimed in Claim 21 to laminate fibre glass sheets.

25. Tanks, pipes or other acid-resistant plant items made from fibre glass reinforcing material laminated with the sulphur cement claimed in Claim 21.

26. Laminated products substantially as hereinbefore described in Example 4 of the foregoing Examples.